grep_cli/
hostname.rs

1use std::{ffi::OsString, io};
2
3/// Returns the hostname of the current system.
4///
5/// It is unusual, although technically possible, for this routine to return
6/// an error. It is difficult to list out the error conditions, but one such
7/// possibility is platform support.
8///
9/// # Platform specific behavior
10///
11/// On Windows, this currently uses the "physical DNS hostname" computer name.
12/// This may change in the future.
13///
14/// On Unix, this returns the result of the `gethostname` function from the
15/// `libc` linked into the program.
16pub fn hostname() -> io::Result<OsString> {
17    #[cfg(windows)]
18    {
19        use winapi_util::sysinfo::{get_computer_name, ComputerNameKind};
20        get_computer_name(ComputerNameKind::PhysicalDnsHostname)
21    }
22    #[cfg(unix)]
23    {
24        gethostname()
25    }
26    #[cfg(not(any(windows, unix)))]
27    {
28        Err(io::Error::new(
29            io::ErrorKind::Other,
30            "hostname could not be found on unsupported platform",
31        ))
32    }
33}
34
35#[cfg(unix)]
36fn gethostname() -> io::Result<OsString> {
37    use std::os::unix::ffi::OsStringExt;
38
39    // SAFETY: There don't appear to be any safety requirements for calling
40    // sysconf.
41    let limit = unsafe { libc::sysconf(libc::_SC_HOST_NAME_MAX) };
42    if limit == -1 {
43        // It is in theory possible for sysconf to return -1 for a limit but
44        // *not* set errno, in which case, io::Error::last_os_error is
45        // indeterminate. But untangling that is super annoying because std
46        // doesn't expose any unix-specific APIs for inspecting the errno. (We
47        // could do it ourselves, but it just doesn't seem worth doing?)
48        return Err(io::Error::last_os_error());
49    }
50    let Ok(maxlen) = usize::try_from(limit) else {
51        let msg = format!("host name max limit ({}) overflowed usize", limit);
52        return Err(io::Error::new(io::ErrorKind::Other, msg));
53    };
54    // maxlen here includes the NUL terminator.
55    let mut buf = vec![0; maxlen];
56    // SAFETY: The pointer we give is valid as it is derived directly from a
57    // Vec. Similarly, `maxlen` is the length of our Vec, and is thus valid
58    // to write to.
59    let rc = unsafe {
60        libc::gethostname(buf.as_mut_ptr().cast::<libc::c_char>(), maxlen)
61    };
62    if rc == -1 {
63        return Err(io::Error::last_os_error());
64    }
65    // POSIX says that if the hostname is bigger than `maxlen`, then it may
66    // write a truncate name back that is not necessarily NUL terminated (wtf,
67    // lol). So if we can't find a NUL terminator, then just give up.
68    let Some(zeropos) = buf.iter().position(|&b| b == 0) else {
69        let msg = "could not find NUL terminator in hostname";
70        return Err(io::Error::new(io::ErrorKind::Other, msg));
71    };
72    buf.truncate(zeropos);
73    buf.shrink_to_fit();
74    Ok(OsString::from_vec(buf))
75}
76
77#[cfg(test)]
78mod tests {
79    use super::*;
80
81    #[test]
82    fn print_hostname() {
83        println!("{:?}", hostname().unwrap());
84    }
85}
grep_cli/hostname.rs

grep_cli/
hostname.rs
